1. Field of Invention
The invention relates to the field of designing and manufacturing a wire harness. Such a wire harness may be used as part of the electrical system of a vehicle, such as an automobile.
More particularly, the invention attempts to determine the appropriate length of each electric wire of the wire harness, without making a large number of experimental trials.
2. Description of Related Art
A wire harness is manufactured by a procedure including the following steps, (1)-(7):
(1) For each new model of vehicle, or for each new version of a pre-existing vehicle, a car maker uses a computer to design a wire harness by a three-dimensional design process. The harness is designed with the requirement that it can be installed in the interior of a vehicle body. PA1 (2) The designed three-dimensional wire harness is then transformed into two-dimensional data. The two-dimensional data further includes data which defines the intended positions of materials for protecting the electric wires, and the interval between branched electric wires of the wire harness. PA1 (3) The car maker sends a wire harness maker a circuit list (that is, a list of circuit components to be installed on a car body) and data defining the connectors to be installed on termination portions of the wire harness. PA1 (4) Based on the data, the wire harness maker calculates the lengths of electric wires for use in constructing the harness (i.e. the wire harness maker calculates the intervals at which a long length of electric wire should be cut in order to supply electric wires for use in the wire harness). The wire harness maker also prepares an assembly drawing, which (as explained below) is used during the assembly of the harness to prevent the electric wires from projecting over the edge of a table on which the wire harness is assembled. PA1 (5) Electric wires are cut based on the calculated lengths, and a terminal is crimped onto an end portion of each electric wire by a terminal-crimping device. PA1 (6) An operator sub-assembles (temporarily binds) the electric wires to one another. In the finished wire harness the ends of some of the wires should be located within a respective connector (the connector having a housing to receive the end), and the operator inserts the end portion of these wires into these respective connector housings during this step. PA1 (7) Finally, the operator correctly places the sub-assembled bundles of electric wires on the table used for assembling the wire harness, combines the sub-assembled bundles with one another, and then binds a plurality of bundles together with adhesive tape. Then, any additional electric components are installed at respective required positions. In this manner, the production of the wire harness is completed. PA1 (1) cutting electric wires of the appropriate lengths, PA1 (2) temporarily binding groups of said electric wires together, PA1 (3) passing the groups through at least one jig on a wire harness assembly platform, PA1 (4) binding the groups to each other by winding adhesive tape around them, and PA1 (5) inserting the ends of a plurality of the wires into respective cavities in connector housings. PA1 k is the number of 2-finger jigs through which the wire passes, PA1 h is the number of 3-finger jigs through which the wire passes, PA1 i is the number of 4-finger jigs through which the wire passes, PA1 m, n and p are integer variables, PA1 W.sub.2,m is the distance between the two fingers of the m-th 2-finger jig, PA1 W.sub.3,p is the distance between two fingers of the p-th 3 finger jig, PA1 W.sub.4,n is the distance between the two fingers of n-th 4finger jig, PA1 r is the radius of the wire, PA1 coe(r) is the minimum radius of curvature of the wire depending on the radius r, and PA1 B is the total number of turns made by the wire due to the jigs. PA1 X and Y are the coordinates of a centre of the wire harness measured along respective x- and y- coordinate axes which are perpendicular to the extension direction and to each other, and PA1 X.sub.1 and Y.sub.1 are the coordinates of the centre of the cavity measured along said respective x- and y- coordinate axes. PA1 (1) cutting electric wires of said appropriate lengths, PA1 (2) temporarily binding groups of electric wires together, PA1 (3) passing the groups through one or more jigs on a wire harness assembly platform, PA1 (4) binding the groups to each other by winding adhesive tape around them, and PA1 (5) inserting the ends of a plurality of the wires into respective cavities in connector housings, PA1 (1) determining an approximate length of each said wire based on an intended path of the respective wire through the wire harness; PA1 (2) determining an appropriate length of each said wire by correcting the respective approximate length to take into account PA1 (3) producing electric wires of said respective appropriate lengths, PA1 (4) temporarily binding groups of electric wires together, PA1 (5) passing the groups through said jigs on a wire harness assembly platform, PA1 (6) binding the groups to each other by winding adhesive tape around them, and PA1 (7) for each wire which has an end which is intended to be inserted into a cavity in a respective connector housing, inserting the end of the wire into said respective cavity in said respective connector housing.
As part of step (7), as illustrated in FIG. 1, in order to straighten the electric wires an operator draws some of the groups of electric wires by hand in a direction away from their connectors (i.e. away from the ends of the electric wires), and then binds the straightened parts of the electric wires together with adhesive tape (T). The reason why the operator binds the electric wires starting at the end nearest the connectors is to ensure that the position of the end of each wire agrees with the length indicated on the assembly drawing, at least to within a certain tolerance. If instead the operator were to bind the electric wires starting at an inner part of the wire harness and work towards the connectors, then the electric wire would be much too long at the connector (i.e. the position of the end would differ from the position indicated on the assembly drawing by more than the tolerance).
Because the operator binds the wires by starting at the outside of the harness and gradually working towards the internal parts of the harness, any excess in the length of a wire causes the wire to flex outwards at an internal branch point of the wire harness.
More specifically, the wires are retained in position in the wire harness by jigs. Among the jigs are jigs having two fingers for retaining wires ("U-shaped jigs"), jigs having three fingers for retaining wires ("Y-shaped jigs"), and jigs having four fingers for retaining wires ("X-shaped jigs"). The fingers extend perpendicularly to the plane of the wire harness assembly platform. As the operator gradually winds the tape around the group of the electric wires starting at the connectors, the operator reaches a point in the wire harness at which a U-shaped, X-shaped or Y-shaped jig (G) supports the group of the electric wires. If the length of the group of electric wires exceeds a tolerance, the excess bulges out between jigs G-1 and G-2, as shown in FIG. 2A.
As shown in FIGS. 2A, 2B, and 2C, the excess electric wire is flexed or coiled before the adhesive tape T is wound on it. At portions of the wire harness at which there are many bundled electric wires, it is necessary to do this many times.
Each such processing step increases the time and labor required to produce the wire harness.
Furthermore, at portions of the wire harness at which many electric wires have been flexed or coiled in this way, the outer diameter of the harness becomes large, and thus the electric wires may interfere with any other nearby components. Therefore, the electric wires should not all be flexed or coiled at the same place. A skilled operator is required to perform such work. Furthermore, because the electric wires are longer than is required, the cost of the resulting wire harness is unnecessarily high, and vehicles on which they are mounted are unnecessarily heavy.
In order to avoid bulging of the electric wires, wire harness manufacturers construct the wire harnesses several times on an experimental basis, to determine an appropriate length of each electric wire. This operation is called "wire length tuning" and is performed two to three times, which takes a considerable time. Thus, it would be advantageous to eliminate the need for the wire length tuning, or at least reduce the number of times wire length tuning must be performed.
Accordingly, the inventors have researched into the procedure for designing wire harnesses by experiment, and found that the excess length of an electric wire arises when the electric wire passes in a curve through a jig. That is, as shown in FIGS. 3A and 3B, the length of an electric wire has been calculated by supposing that in passing through the jig, the electric wire lies in the plane of a wire harness, and, if for instance the jig G includes two fingers Gb and Gc upstanding from a wire holding portion Ga, that the wire passes through the center of the interval between fingers Gb and Gc. It is also assumed that the electric wire bends by 90.degree. at the center of the interval between the fingers Gb and Gc. These assumptions are applied to calculate the length of each electric wire, and as a result, the calculated length of the electric wire is too long, due to the fact that the wire actually curves and is displaced from the center of the interval between the fingers. The over-calculation is great if the jig is large, i.e. when the interval between the fingers Gb and Gc is large, or if the electric wire passes through many jigs.